What indicates moderate to severe dehydration in a 3-month-old infant with rotavirus?

The presence of a sunken anterior fontanel in a 3-month-old infant is a significant indicator of moderate to severe dehydration. The anterior fontanel, the soft spot on the top of an infant's head, is normally slightly rounded or flat. When dehydration occurs, the body loses fluids, which can lead to a decrease in blood volume and pressure. This may cause the fontanel to appear sunken as the surrounding tissues lose moisture.

In infants, the status of the anterior fontanel can be a vital sign for assessing hydration levels. A sunken fontanel indicates that the infant is likely experiencing dehydration and may require medical intervention. This is particularly relevant in cases like a rotavirus infection, which can lead to severe vomiting and diarrhea, exacerbating fluid loss.

Other signs of dehydration in infants may include dry mucous membranes, decreased urine output, and lethargy, but the sunken fontanel specifically indicates a more severe level of dehydration and should prompt immediate evaluation and treatment.